Reliability of a novel electro‐medical device for wheal size measurement in allergy skin testing: An exploratory clinical trial
Authors: María de la Paz Morales‐Palacios, Jorge M. Núñez‐Córdoba, Eduardo Tejero, Óscar Matellanes, Paola Leonor Quan, Álvaro Carvallo, Sergio Sánchez‐Fernández, Maite Urtasun, Carla Larrea, María Teresa Íñiguez, Rosa Giménez, Maria José Goikoetxea, Carmen M. D'Amelio, Marta Ferrer, Gabriel Gastaminza
Journal: Allergy (2022)

Skin prick testing (SPT) is the cornerstone of IgE-mediated allergy diagnosis,1 due to its high sensitivity and specificity.2 However, a uniform method for wheal measurement does not exist. Ansotegui et al.2 recommends to measure wheals in millimeters with a ruler, in many centers they are outlined with a pen and transfer by tape to a paper and then measured. Subsequently, the specialist is able to manually measure the maximum (MD) and orthogonal diameter (OD) of the wheal. This procedure is time consuming and makes reproducible measurements difficult.2, 3 Knowing the wheal's area could help make a more accurate diagnosis.4 Over the last 30 years, many attempts have been made to develop a device to measure the size of SPT.3 Nexkin DSPT® (Figure S1A,B) is a novel mechatronic system based on 3D laser technology, that automatically locates allergen's wheal and measures its size (MD, OD and area in square millimeters) (Figure S1C). A prospective clinical trial was conducted at Clínica Universidad de Navarra (NCT05284565) to evaluate the level of agreement in wheal size measures between this new device and the manual procedure, to assess the test–retest reliability for both procedures, and to compare reading value variations between both measurement approaches. Methods details are shown in Appendix S1. A total of 108 individuals were screened during the study period (Figure S2) and 93 patients were finally included for analysis. SPT was performed with positive (histamine) and negative (saline solution) controls. Fifteen minutes later, two consecutive readings with the device and two manual readings were performed by two separate nurses. Comparisons between first and second readings are shown in Table S1. Correlations between the manual procedure and the device (Figure 1) showed a relatively strong association, and all of them were statistically significant (Area: r = .742, p < .001; MD, r = .700, p < .001; OD, r = .644, p < .001). The intraclass correlation coefficient (ICC) values showed poor to moderate agreement between the manual procedure and the device [0.49 (95% CI: 0.26–0.65) to 0.70 (95% CI: 0.53–0.81)]. Test–retest reliability (Figure S3) was found to be moderate to good for the manual procedure (ICC values ranged from 0.57 [95% CI: 0.42–0.70] to 0.80 [95% CI: 0.71–0.86], corresponding to OD and area evaluations, respectively) and good to excellent for the device (the ICC values were 0.88 [95% CI: 0.83–0.92] in area, 0.85 [95% CI: 0.79–0.90] in MD, and 0.85 [95% CI: 0.78–0.90] in OD). The consistency of Nexkin DSPT® readings appeared to be greater than those of the manual procedure. Reading variations in area (Figure 2) for Nexkin DSPT® (2.02 mm2; SD = 3.42) were lower than those of the manual procedure (4.94 mm2; SD = 4.14) (p < .001). Similar results were obtained for MD and OD of wheals. Additional results are included in Appendix S1. Overall, the agreement between the device and manual procedure was moderate. Although no gold standard method exists,5 the automatic measurement system of the device seems to be more appropriate to yield less variable measurements than the manual procedure, as the results from the device are regardless of the individual who performs SPT and/or the thickness of the pen used to outline the wheals.6 The discussion was expanded in Appendix S1. The results suggest a higher reliability of the electro-medical device Nexkin DSPT® for the measurement of wheal area in SPT, compared to the manual procedure. This device has potential for improving the uniformity of the reading phase of the SPT and, therefore, it may favour standardization, upgrade, and innovation of the current SPT technique. We wish to thank Mr. Gustavo Pego, from Innovation Factory of the University of Navarra, for promoting this project. GG is a member of the Nexkin Medical advisory board and patent's co-author: Measuring Wheals and Detecting Allergies. OM and ET are Nexkin Medical employees and shareholders. The remaining authors have no conflicts of interests. Appendix S1 Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.